The Giants’ business was not to give Manningham starter money when they already had Hakeem Nicks and Victor Cruz as their established starting receivers, so they moved on and so did Manningham — straight to one of their chief NFC rivals, the 49ers.

So on Sunday when the 49ers host the Giants, Manningham gets his chance to show his former team what it’s missing.

“Oh man, that’s a player’s dream — to go out and beat their old team,’’ Manningham said yesterday. “We play the Dolphins [later this season] and that’s Ted’s [Ted Ginn Jr.] old team. We played Minnesota and play New England and those are Randy [Moss’] old teams. Now my time is up.

“I’m going to go out there and play my butt off, plain and simple. Do I have a grudge? No. But am I motivated? Yes. I’m motivated by this game. Who wouldn’t be motivated by playing their old team?’’

Manningham, who spent his first four NFL seasons with the Giants, said he loves his new home, saying, “I couldn’t ask for a better team, better teammates, a better coaching staff, better equipment managers, everybody else.

“It’s worked out more than I thought it was going to work out. I’m blessed to be in this situation. I left a good team and went to [another] good team.’’

Manningham sounded delighted about being a starter in San Francisco instead of the No. 3 had he re-signed with the Giants.

“I’m involved more over here,’’ he said. “I knew [the 49ers] needed help at receiver — not saying they were terrible, but that’s why I came over here trying to contribute.’’

Manningham is third on the 49ers with 19 receptions for 186 yards and a touchdown and has run two reverses — one for 29 yards and one for 28.

“He’s been consistently good in the way of blocking, route running, catching the football and as a runner as well — not just consistent, but consistently good,’’ 49ers head coach Jim Harbaugh said.

“He’s been effective with what they have him doing — with reverses, trying to get the ball in his hands fast and let him wiggle in space … what Mario does best,’’ Giants safety Antrel Rolle said.

Manningham indicated he has been schooling his current teammates on the tendencies of his former teammates, including Eli Manning,saying, “I’ve talked to my teammates and given them some heads up on what going to happen. I know what’s going on and I shared it with them.’’

Manning sounded unconcerned.

“I think we’ll be all right,’’ he said. “Everybody always talks a little bit, but they’re not going to know what plays we’re running or what we’re doing.’’Giants cornerback Prince Amukamara said on Monday he heard Manningham was already stoked about playing his former team, saying, “I heard he’s already talking.’’

Asked where he heard that, Amukamara smiled and got cryptic, saying, “Ah, just from a friend. Just that he’s excited to play us.’’